Recently developed switching elements (see, for example, JP2005-101535A) can be programmably set to a high-resistance state and a low-resistance state, can store the set state in a non-volatile manner, and can exhibit a significantly low on-resistance as compared with a MOS transistor having the same footprint area (hereinafter referred to as the “variable resistance switching element”).
FIG. 1 is a diagram showing an exemplary configuration of a variable resistance switching element.
Variable resistance switching element 10 shown in FIG. 1 comprises source electrode 20, drain electrode 21, and ion conduction layer 22. Source electrode 20 is an electrode for supplying a metal ion, and is made, for example, of copper or the like. Drain electrode 21 is an electrode which does not supply a metal ion, and is made, for example, of platinum or the like. Ion conduction layer 22 is made, for example, of tantalum oxide.
FIG. 2(a) is a diagram showing the operation of variable resistance switching element 10 shown in FIG. 1 when source electrode 20 is applied with write voltage Vp, and drain electrode 21 is set at voltage 0.
For making variable resistance switching element 10 conductive between source electrode 20 and drain electrode 21 from a shut-off state, source electrode 20 is applied with write voltage Vp, and drain electrode 21 is set to voltage 0, as shown in FIG. 2(a). In this way, precipitated metal 25 is precipitated from drain electrode 21 toward source electrode 20, and after the lapse of a certain time, variable resistance switching element 10 is made conductive between the two electrodes by the action of this precipitated metal 25.
FIG. 2(b) is a diagram showing the operation of variable resistance switching element 10 in the state shown in FIG. 2(a), when source electrode 20 is set to voltage 0, and drain electrode 21 is applied with voltage Vp.
To again bring the conduction between source electrode 20 and drain electrode 21 into a shut-off state, source electrode 20 is set to voltage 0, and drain electrode 21 is applied with voltage Vp, as shown in FIG. 2(b). When a certain time elapses in this state, the aforementioned precipitated metal 25 disappears, causing variable resistance switching element 10 to put both electrodes into shut-off state.
FIG. 3 is a diagram showing an exemplary configuration of a semiconductor device which comprises a reconfigurable wiring network using variable resistance switching elements 10 shown in FIG. 1.
The reconfigurable wiring network shown in FIG. 3 comprises wiring segments 4XY arranged in an array form, where wiring segments 4Xa, 4Xb, 4Xc, . . . arranged on the same axis in the horizontal direction are programmably coupled to adjacent wiring segments, respectively, through variable resistance switching elements 10Xa, 10Xb, 10Xc, . . . (where X, Y are variables representative of a, b, c, . . . ).
Assume that a lane refers to a sequence of wiring segments 4XY and variable resistance switching elements 10XY arranged on the same axis in the horizontal direction. FIG. 3 shows three exemplary lanes which include a lane extending from wiring segment 4aa to wiring segment 4ae, a lane extending from wiring segment 4ba to wiring segment 4be, and a lane extending from wiring segment 4ca to wiring segment 4ce. 
Each variable resistance switching element 10XY is associated with MOS transistor 2XY, such that the source and drain of MOS transistor 2XY are connected to the respective electrodes of variable resistance switching element 10XY, respectively. MOS transistors 2aY, 2bY, 2cY, . . . arranged in the vertical direction have their gates connected to common gate line 3Y.
In the reconfigurable wiring network shown in FIG. 3, a configuration is set up in the following manner for setting the states of variable resistance switching elements 10XY in a desired pattern to connect or shut off wiring segments 4XY.
An OFF voltage is applied to the gate of a MOS transistor associated with variable resistance switching element 10XY for which a configuration is to be set up, to bring the MOS transistor into a shut-off state between its source and drain electrodes. Simultaneously, an ON voltage is applied to the gates of the remaining MOS transistors to bring them into a conductive state between their source and drain electrodes. Since a gate voltage is applied through gate line 3Y, MOS transistors 2XY are controlled ON/OFF in units of columns arranged in the vertical direction.
Next, when conduction state is to be established between the electrodes of variable resistance switching elements 10XY associated with MOS transistors 2XY which have been turned OFF, voltages are applied to both ends of an associated lane for state setup. Specifically, write voltage Vp is applied to a left end of the line, while a zero-voltage is applied to a right end of the same for bringing variable resistance switching element 10XY into a conductive state.
On the other hand, write voltage Vp is applied to the right end of the lane, while zero-voltage is applied to the left end of the same, to bring variable resistance switching element 10XY into a shut-off state.
Assume herein that the source electrode is positioned on the left side of variable resistance switching element 10XY, and the drain electrode is positioned on the right side of the same, as shown in FIG. 3. Notably, when it is not necessary to change the state of variable resistance switching element 10XY, both ends of an associated lane are set at the same voltage.
The operation in which variable resistance switching elements 10XY are configured is performed for every gate line 3Y. Specifically, all variable resistance switching elements 10XY corresponding to one gate line are subjected to the state setup at one time, and such an operation is sequentially performed for each gate line 3Y. In this way, the configuration is fully accomplished.
In the example described above, voltages are applied from both ends of a lane for configuring particular variable resistance switching elements 10XY, so that all variable resistance switching elements 10XY are provided with MOS transistors 2XY for bypassing them. While variable resistance switching element 10XY itself is very small as compared with MOS transistor 2XY, these MOS transistors 2XY for bypassing cause the circuit area of the overall semiconductor device to increase.
The semiconductor device and configuration method as described above imply a problem that a circuit area increases. This is because a MOS transistor must be provided for each variable resistance switching element for bypassing.